Optical imaging system

ABSTRACT

An optical imaging system includes lenses sequentially disposed from an object side toward an imaging plane and including a refractive power in paraxial regions or edges of the paraxial regions. An object-side surface of a fifth lens of the lenses is planar in a paraxial region and the fifth lens includes a refractive power at an edge of the paraxial region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/695,885 filed on Nov. 26, 2019, which is a continuation of U.S.patent application Ser. No. 15/950,775 filed on Apr. 11, 2018, now U.S.Pat. No. 10,527,823 issued on Jan. 7, 2020, which is a continuation ofU.S. patent application Ser. No. 15/138,780 filed on Apr. 26, 2016, nowU.S. Pat. No. 9,971,125 issued on May 15, 2018, which claims the benefitunder 35 USC § 119(a) of Korean Patent Application No. 10-2015-0164972filed on Nov. 24, 2015, in the Korean Intellectual Property Office, theentire disclosures of which are incorporated herein by reference for allpurposes.

BACKGROUND 1. Field

The following description relates to an optical imaging system includinglenses.

2. Description of Related Art

Normally, a small camera module is mounted in a portable terminal, suchas a mobile device or a tablet. The small camera module includes four orfive lenses to realize an optical imaging system having a high level ofresolution. However, as a result of a gradual increase in a number ofpixels of an image sensor capturing images of a subject in the cameramodule, an optical imaging system that is able to capture the image ofthe subject much brighter than an existing optical imaging system is indemand.

Therefore, there is a need to develop an optical imaging system capableof being mounted in the small camera and having an F number of 2.0 orless.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In accordance with an embodiment, there is provided an optical imagingsystem, including: lenses sequentially disposed from an object sidetoward an imaging plane and including a refractive power in paraxialregions or edges of the paraxial regions, wherein an object-side surfaceof a fifth lens of the lenses is planar in a paraxial region and thefifth lens may include a refractive power at an edge of the paraxialregion.

A first lens of the lenses may include a positive refractive power.

A second lens of the lenses may include a positive refractive power.

A third lens of the lenses may include a negative positive power.

A fourth lens of the lenses may include a positive refractive power.

A sixth lens of the lenses may include a negative refractive power.

A sixth lens of the lenses may include an aspherical shape in which oneor more inflection points are formed on an image-side surface thereof.

The optical imaging system may also include a stop disposed between asecond lens and a third lens of the lenses.

0.05<Th5/f<0.25 may be satisfied, in which Th5 is a thickness of anoptical axis center of the fifth lens, and f is an overall focal lengthof the optical imaging system.

20<V1−V3<70 may be satisfied, in which V1 is an Abbe number of a firstlens of the lenses, and V3 is an Abbe number of a third lens of thelenses.

|Sag51/Th5|<1.0 may be satisfied, in which Sag51 is a Sag value at anend of an effective diameter of an object-side surface of the fifthlens, and Th5 is a thickness of an optical axis center of the fifthlens.

−1.5<f3/f2 may be satisfied, in which f2 is a focal length of a secondlens of the lenses, and f3 is a focal length of a third lens of thelenses.

0.5<OAL/f<2.0 may be satisfied, in which OAL is a distance from anobject-side surface of a first lens of the lenses toward the imagingplane, and f is an overall focal length of the optical imaging system.

1.6<n5<2.1 may be satisfied, in which n5 is a refractive index of thefifth lens.

F number<2.0 may be satisfied.

In accordance with an embodiment, there is provided an optical imagingsystem, including: a first lens including a convex object-side surface;a second lens including a convex object-side surface and a conveximage-side surface; a third lens including a convex object-side surface;a fourth lens including a convex object-side surface; a fifth lensincluding a planar surface on a paraxial region thereof; and a sixthlens including a convex object-side surface, wherein the first to sixthlenses are spaced apart and sequentially disposed from an object sidetoward an imaging plane.

In accordance with an embodiment, there is provided an optical imagingsystem, including: a first lens; a second lens; a third lens including aconvex object-side surface; a fourth lens including, in a paraxialregion, a convex object-side surface; a fifth lens including, in theparaxial region, at least one of a planar object-side surface and aplanar image-side surface; and a sixth lens, wherein the third lens, thefourth lens, and the fifth lens may include a same refractive index.

The first lens, the second lens, and the sixth lens may include a samerefractive index, different from the refractive index of the third lens,the fourth lens, and the fifth lens.

The first lens may include a convex object-side surface, the second lensmay include a convex object-side surface and a convex image-sidesurface, and the sixth lens may include, in the paraxial region, aconvex object-side surface and a concave image-side surface.

The object-side surface of the fourth lens gradually concaves at edgeportions thereof.

The image-side surface of the fourth lens is convex in the paraxialregion.

The image-side surface of the fourth lens is concave in the paraxialregion.

Inflection points may be formed on the object-side surface and theimage-side surface of the sixth lens.

The fifth lens excludes a refractive power in a paraxial region thereof.

In accordance with an embodiment, there is provided an optical imagingsystem, including: a first lens including a positive refractive power; asecond lens including a positive refractive power; a third lensincluding a negative refractive power; a fourth lens including apositive refractive power; and a fifth lens of the lenses including, ina paraxial region, at least one planar side surface excluding arefractive power, and a sixth lens including a negative refractivepower, wherein the first through sixth lenses satisfy F number<2.0.

0.05<Th5/f<0.25 may be satisfied, in which Th5 is a thickness of anoptical axis center of the fifth lens, and f is an overall focal lengthof the optical imaging system.

20<V1−V3<70 may be satisfied, in which V1 is an Abbe number of the firstlens, and V3 is an Abbe number of the third lens.

|Sag51/Th5|<1.0 may be satisfied, in which Th5 is a thickness of anoptical axis center of the fifth lens, and Sag51 is a Sag value at anend of an effective diameter of an object-side surface of the fifthlens.

−1.5<f3/f2 may be satisfied, in which f2 is a focal length of the secondlens, and f3 is a focal length of the third lens.

0.5<OAL/f<2.0 may be satisfied, in which OAL is a distance from theobject-side surface of the first lens toward the imaging plane, and f isan overall focal length of the optical imaging system.

1.6<n5<2.1 may be satisfied, in which n5 is a refractive index of thefifth lens.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a view of an optical imaging system, according to a firstembodiment;

FIG. 2 is graphs representing aberration curves of the optical imagingsystem illustrated in FIG. 1;

FIG. 3 is a table representing characteristics of lenses of the opticalimaging system illustrated in FIG. 1;

FIG. 4 is a view of an optical imaging system, according to a secondembodiment;

FIG. 5 is graphs representing aberration curves of the optical imagingsystem illustrated in FIG. 4;

FIG. 6 is a table representing characteristics of lenses of the opticalimaging system illustrated in FIG. 4;

FIG. 7 is a view of an optical imaging system, according to a thirdembodiment;

FIG. 8 is graphs representing aberration curves of the optical imagingsystem illustrated in FIG. 7; and

FIG. 9 is a table representing characteristics of lenses of the opticalimaging system illustrated in FIG. 7.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals will be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/ormethods described herein will be apparent to one of ordinary skill inthe art. For example, the sequences of operations described herein aremerely examples, and are not limited to those set forth herein, but maybe changed as will be apparent to one of ordinary skill in the art, withthe exception of operations necessarily occurring in a certain order.Also, descriptions of functions and constructions that are well known toone of ordinary skill in the art may be omitted for increased clarityand conciseness.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided so thatthis disclosure will be thorough and complete, and will convey the fullscope of the disclosure to one of ordinary skill in the art.

Throughout the specification, it will be understood that when anelement, such as a layer, region or wafer (substrate), is referred to asbeing “on,” “connected to,” or “coupled to” another element, it can bedirectly “on,” “connected to,” or “coupled to” the other element orother elements intervening therebetween may be present. In contrast,when an element is referred to as being “directly on,” “directlyconnected to,” or “directly coupled to” another element, there may be noelements or layers intervening therebetween. Like numerals refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be apparent that though the terms first, second, third, etc. maybe used herein to describe various members, components, regions, layersand/or sections, these members, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one member, component, region, layer or section fromanother region, layer or section. Thus, a first member, component,region, layer or section discussed below could be termed a secondmember, component, region, layer or section without departing from theteachings of the embodiments.

Spatially relative terms, such as “above,” “upper,” “below,” and“lower”, may be used herein for ease of description to describe oneelement's relationship to another element(s) as shown in the figures. Itwill be understood that the spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. For example, if thedevice in the figures is turned over, elements described as “above,” or“upper” other elements would then be oriented “below,” or “lower” theother elements or features. Thus, the term “above” can encompass boththe above and below orientations depending on a particular direction ofthe figures. The device may be otherwise oriented (rotated 90 degrees orat other orientations) and the spatially relative descriptors usedherein may be interpreted accordingly.

The terminology used herein is for describing various embodiments onlyand is not intended to be limiting of the present inventive concept. Asused herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”and/or “comprising” when used in this specification, specify thepresence of stated features, integers, steps, operations, members,elements, and/or groups thereof, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,members, elements, and/or groups thereof.

Hereinafter, various embodiments will be described with reference toschematic views. In the drawings, for example, due to manufacturingtechniques and/or tolerances, modifications of the shape shown may beestimated. Thus, embodiments should not be construed as being limited tothe particular shapes of regions shown herein, for example, to include achange in shape results in manufacturing. The following embodiments mayalso be formed by one or a combination thereof.

In addition, in accordance with an embodiment, a first lens refers to alens closest to an object or a subject from which an image is captured.A sixth lens is a lens closest to an imaging plane or an image sensor.In addition, all of radii of curvature and thicknesses of lenses, anOAL, an Img HT (½ of a diagonal length of the imaging plane), and focallengths are indicated in millimeters (mm).

A person skilled in the relevant art will appreciate that other units ofmeasurement may be used. Further, in the present specification, allradii of curvature, thicknesses, OALs (optical axis distances from thefirst surface of the first lens to the image sensor (OALs), a distanceon the optical axis between the stop and the image sensor (SLs), imageheights (IMGHs) (image heights), and black focus lengths (BFLs) (backfocus lengths) of the lenses, an overall focal length of an opticalsystem, and a focal length of each lens are indicated in millimeters(mm). Further, thicknesses of lenses, gaps between the lenses, OALs, andSLs are distances measured based on an optical axis of the lenses.

Further, concerning shapes of the lenses, such shapes are represented inrelation to optical axes of the lenses. A surface of a lens being convexmeans that an optical axis portion of a corresponding surface is convex,and a surface of a lens being concave means that an optical axis portionof a corresponding surface is concave. Therefore, in a configuration inwhich one surface of a lens is described as being convex, an edgeportion of the lens may be concave. Likewise, in a configuration inwhich one surface of a lens is described as being concave, an edgeportion of the lens may be convex. In other words, a paraxial region ofa lens may be convex, while the remaining portion of the lens outsidethe paraxial region is either convex, concave, or flat. Further, aparaxial region of a lens may be concave, while the remaining portion ofthe lens outside the paraxial region is either convex, concave, or flat.

In addition, in an embodiment, thicknesses and radii of curvatures oflenses are measured in relation to optical axes of the correspondinglenses.

An optical system, according to an embodiment, includes six lenses. Asan example, the optical system may include a first lens, a second lens,a third lens, a fourth lens, a fifth lens, and a sixth lens. The lensmodule may include from four lenses up to six lenses without departingfrom the scope of the embodiments herein described. In accordance withan illustrative example, the embodiments described of the optical systeminclude six lenses with a refractive power. However, a person ofordinary skill in the relevant art will appreciate that the number oflenses in the optical system may vary, for example, between two to sixlenses, while achieving the various results and benefits describedhereinbelow. Also, although each lens is described with a particularrefractive power, a different refractive power for at least one of thelenses may be used to achieve the intended result.

The first lens has a refractive power. For example, the first lens has apositive refractive power.

One surface of the first lens is convex. For example, an object-sidesurface of the first lens is convex.

The first lens has an aspherical surface. For example, both surfaces ofthe first lens are aspherical. The first lens may be formed of amaterial having high light transmissivity and excellent workability. Forexample, the first lens is formed of plastic or a polyurethane material.However, a material of the first lens is not limited to plastic. Forexample, the first lens may be formed of glass.

The second lens has a refractive power. For example, the second lens hasa positive refractive power.

At least one surface of the second lens is convex. For example, bothsurfaces of the second lens are convex.

The second lens has an aspherical surface. For example, an object-sidesurface of the second lens is aspherical. The second lens is formed of amaterial having high light transmissivity and excellent workability. Forexample, the second lens may be formed of plastic or a polyurethanematerial. However, a material of the second lens is not limited toplastic. For example, the second lens may be formed of glass.

The third lens has a refractive power. For example, the third lens has anegative refractive power.

One surface of the third lens is convex. For example, an object-sidesurface of the third lens is convex. In an alternative embodiment, thefirst surface or the object-side surface of the third lens is flat orsubstantially flat and the second surface or the image-side surface isconcave.

The third lens has an aspherical surface. For example, both surfaces ofthe third lens are aspherical. The third lens is formed of a materialhaving high light transmissivity and excellent workability. For example,the third lens may be formed of plastic or a polyurethane material.However, a material of the third lens is not limited to plastic. Forexample, the third lens may be formed of glass.

The fourth lens has a refractive power. For example, the fourth lens hasa positive refractive power.

One surface of the fourth lens is convex. For example, an object-sidesurface of the fourth lens is convex. In one example, the object-sidesurface of the fourth lens is convex in a paraxial region and graduallyconcaves at edge portions thereof. In another example, the image-sidesurface of the fourth lens is convex in a paraxial region. In anotherexample, the image-side surface of the fourth lens is concave in aparaxial region.

The fourth lens has an aspherical surface. For example, both surfaces ofthe fourth lens are aspherical. The fourth lens is formed of a materialhaving high light transmissivity and excellent workability. For example,the fourth lens is formed of plastic or a polyurethane material.However, a material of the fourth lens is not limited to plastic. Forexample, the fourth lens may be formed of glass.

The fifth lens has refractive power. For example, the fifth lens mayhave a positive refractive power or a negative refractive power in anedge of a paraxial region thereof.

The fifth lens is partially flat or substantially flat. For example, thefifth lens may be planar in the paraxial region thereof. In one example,the object-side surface of the fifth lens is flat in a paraxial regionand gradually concaves at edge portions thereof. In another example, theimage-side surface of the fifth lens is flat or substantially flat in aparaxial region and gradually curves, in a convex shape, at edgeportions thereof.

The fifth lens has an aspherical surface. For example, both surfaces ofthe fifth lens are aspherical. The fifth lens is formed of a materialhaving high light transmissivity and excellent workability. For example,the fifth lens is formed of plastic or a polyurethane material. However,a material of the fifth lens is not limited to plastic. For example, thefifth lens may be formed of glass.

The sixth lens has a refractive power. For example, the sixth lens has anegative refractive power.

One surface of the sixth lens is convex. For example, an object-sidesurface of the sixth lens is convex. The sixth lens has inflectionpoints. For example, one or more inflection points are formed on anobject-side surface and an image-side surface of the sixth lens.

The sixth lens has an aspherical surface. For example, both surfaces ofthe sixth lens are aspherical. The sixth lens is formed of a materialhaving high light transmissivity and excellent workability. For example,the sixth lens may be formed of plastic. However, a material of thesixth lens is not limited to plastic or a polyurethane material. Forexample, the sixth lens may be formed of glass.

In an embodiment, the image-side surface of the sixth lens is concave ina paraxial region and gradually curves to be convex towards edgeportions thereof.

A person of ordinary skill in the relevant art will appreciate that eachof the first through sixth lenses may be configured in an oppositerefractive power from the configuration described above. For example, inan alternative configuration, the first lens has a negative refractivepower, the second lens has a negative refractive power, the third lenshas a positive refractive power, the fourth lens has a negativerefractive power, the fifth lens no refractive power, and the sixth lenshas a positive refractive power.

First to sixth lenses are formed of materials having a refractive indexdifferent from that of air. For example, the first to sixth lenses areformed of plastic or glass. At least one of the first to sixth lenseshas an aspherical shape. As an example, all of the first to sixth lenseshave the aspherical shape. In an example, an aspherical surface of eachlens is represented by the following Equation 1:

$\begin{matrix}{Z = {\frac{c\; r^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {A\; r^{4}} + {B\; r^{6}} + {Cr^{8}} + {Dr^{10}} + {Er^{12}} + {F\; r^{14}} + {Gr^{16}} + {Hr^{18}} + {J\;{r^{20}.}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In an example, c is an inverse of a radius of curvature of the lens, kis a conic constant, r is a distance from a certain point on anaspherical surface of the lens to an optical axis, A to J are asphericalconstants, and Z (or SAG) is a distance between the certain point on theaspherical surface of the lens at the distance Y and a tangential planemeeting the apex of the aspherical surface of the lens.

In one embodiment, the optical imaging system includes lenses having thesame refractive index. For example, the third to fifth lenses may havethe same refractive index. In addition, the first lens, the second lens,and the sixth lens may have the same refractive index, different fromthe refractive index of the third to fifth lenses.

The optical imaging system includes a stop. The stop is disposed betweenthe second and third lenses. The stop disposed as described aboveadjusts an amount of light incident to the imaging plane.

The optical imaging system includes a filter. The filter filters apartial wavelength from light incident through the first to sixthlenses. For example, the filter filters an infrared wavelength of theincident light.

The optical imaging system includes an image sensor. The image sensorprovides the imaging plane on which light refracted by the lenses may beimaged. For example, a surface of the image sensor forms the imagingplane. The image sensor is configured to realize a high resolution. Forexample, a unit size of pixels configuring the image sensor may be 1.12μm or less.

Also, in one embodiment, each of the first to sixth lenses may beseparate lenses configured as described above. A distance between lensesmay vary. In another embodiment, at least one of the first to sixthlenses may be operatively connected or in contact with another one ofthe first to sixth lenses.

The optical imaging system satisfies the following ConditionalExpressions 1 through 7:

0.05<Th5/f<0.25  [Conditional Expression 1]

20<V1−V3<70  [Conditional Expression 2]

|Sag51/Th5|<1.0  [Conditional Expression 3]

−1.5<f3/f2  [Conditional Expression 4]

0.5<OAL/f<2.0  [Conditional Expression 5]

1.6<n5<2.1  [Conditional Expression 6]

F number<2.0.  [Conditional Expression 7]

In one example, Th5 is a thickness of an optical axis center of thefifth lens, f is an overall focal length of the optical imaging system,V1 is an Abbe number of the first lens, V3 is an Abbe number of thethird lens, Sag51 is a Sag value at an end of an effective diameter ofan object-side surface of the fifth lens, f2 is a focal length of thesecond lens, f3 is a focal length of the third lens, OAL is a distancefrom the object-side surface of the first lens toward the imaging plane,and n5 is a refractive index of the fifth lens. F number is an angle ofconvergence in a cone of focusing light emanating from a circularaperture. The F number is defined by an effective focal length of theoptical system (f) divided by the optical system's circular entrancepupil diameter (D).

The optical imaging system satisfying the above Conditional Expressions1 through 7 may be miniaturized, and may realize a high resolution.

Next, optical imaging systems, according to various embodiments, will bedescribed.

An optical imaging system, according to a first embodiment, will bedescribed with reference to FIG. 1.

The optical imaging system 100, according to the first embodiment,includes a plurality of lenses having refractive power. For example, theoptical imaging system 100 includes a first lens 110, a second lens 120,a third lens 130, a fourth lens 140, a fifth lens 150, and a sixth lens160.

In accordance with an example, the object-side surfaces and theimage-side surfaces to be described below with respect to each of thefirst through sixth lenses 110 through 160 are described with respect tothe paraxial regions. For instance, for the first lens 110, anobject-side surface thereof is convex in the paraxial region and animage-side surface thereof is concave in the paraxial region. Surfaceregions, on the object-side surface and the image-side surface, whichneighbor or are in the vicinity of the paraxial regions may also havethe same curvature as the corresponding paraxial regions or may beconcave, convex, flat, or substantially flat. The configurationillustrated in FIG. 1 is one illustrative example of the surface regionsin the vicinity of the paraxial regions. However, a person skilled inthe art will appreciate that different curvatures or flatness may beimplemented in the surface regions in the vicinity of the paraxialregions than those illustrated in FIG. 1.

The first lens 110 has a positive refractive power, and an object-sidesurface thereof is convex and an image-side surface thereof is concave.The second lens 120 has a positive refractive power, and an object-sidesurface thereof is convex and an image-side surface thereof is convex.The third lens 130 has a negative refractive power, and an object-sidesurface thereof is convex and an image-side surface thereof is concave.The fourth lens 140 has a positive refractive power, and an object-sidesurface thereof is convex and an image-side surface thereof is convex.The fifth lens 150 may not have a refractive power in a paraxial regionthereof. For example, the fifth lens 150 is planar in the paraxialregion of the object-side surface thereof. The sixth lens 160 has anegative refractive power, and an object-side surface thereof is convexand an image-side surface thereof is concave. In addition, inflectionpoints may be formed on both surfaces of the sixth lens 160. Forexample, the object-side surface of the sixth lens is convex in aparaxial region thereof and concave in a vicinity of the paraxialregion. Similarly, the image-side surface of the sixth lens is concavein a paraxial region thereof and convex in a vicinity of the paraxialregion.

The optical imaging system 100 includes a stop ST. For example, the stopST is disposed between the second lens 120 and the third lens 130. Thestop ST disposed as described above adjusts an amount of light incidentto an imaging plane 180.

The optical imaging system 100 includes a filter 170. For example, thefilter 170 is disposed between the sixth lens 160 and the imaging plane180. The filter 170 disposed as described above filters infrared raysincident to the imaging plane 180.

The optical imaging system 100 includes an image sensor. The imagesensor provides the imaging plane 180 on which light refracted throughthe lenses is imaged. In addition, the image sensor converts an opticalsignal imaged on the imaging plane 180 into an electrical signal.

The optical imaging system configured as described above may representaberration characteristics as illustrated in FIG. 2. FIG. 3 is a tablerepresenting characteristics of lenses of the optical imaging system,according to an embodiment.

An optical imaging system, according to a second embodiment will bedescribed with reference to FIG. 4.

The optical imaging system 200, according to the second embodiment,includes a plurality of lenses having refractive power. For example, theoptical imaging system 200 includes a first lens 210, a second lens 220,a third lens 230, a fourth lens 240, a fifth lens 250, and a sixth lens260.

In accordance with an example, the object-side surfaces and theimage-side surfaces to be described below with respect to each of thefirst through sixth lenses 210 through 260 are described with respect tothe paraxial regions. For instance, for the first lens 210, anobject-side surface thereof is convex in the paraxial region and animage-side surface thereof is concave in the paraxial region. Surfaceregions, on the object-side surface and the image-side surface, whichneighbor or are in the vicinity of the paraxial regions may also havethe same curvature as the corresponding paraxial regions or may beconcave, convex, flat, or substantially flat. The configurationillustrated in FIG. 2 is one illustrative example of the surface regionsin the vicinity of the paraxial regions. However, a person skilled inthe art will appreciate that different curvatures or flatness may beimplemented in the surface regions in the vicinity of the paraxialregions than those illustrated in FIG. 2.

The first lens 210 has a positive refractive power, and an object-sidesurface thereof is convex and an image-side surface thereof is concave.The second lens 220 has a positive refractive power, and an object-sidesurface thereof may be convex and an image-side surface thereof may beconvex. The third lens 230 has a negative refractive power, and anobject-side surface thereof is convex and an image-side surface thereofis concave. The fourth lens 240 has a positive refractive power, and anobject-side surface thereof is convex and an image-side surface thereofis convex. The fifth lens 250 does not have a refractive power in aparaxial region thereof. For example, the fifth lens 250 is planar inthe paraxial region thereof. In one embodiment, the fifth lens 250 isplanar in the paraxial region of the object-side surface thereof and theparaxial region of the image-side surface thereof. In anotherembodiment, the fifth lens 250 is planar in the paraxial region only ofthe object-side surface thereof. In further another embodiment, thefifth lens 250 is planar in the paraxial region only of the image-sidesurface thereof. The sixth lens 260 has a negative refractive power, andan object-side surface thereof may be convex and an image-side surfacethereof may be concave. In addition, inflection points are formed onboth surfaces of the sixth lens 260. For example, the object-sidesurface of the sixth lens is convex in a paraxial region thereof andconcave in the vicinity of the paraxial region. Similarly, theimage-side surface of the sixth lens is concave in a paraxial regionthereof and convex in the vicinity of the paraxial region.

The optical imaging system 200 includes a stop ST. For example, the stopST is disposed between the second lens 220 and the third lens 230. Thestop ST disposed as described above adjusts an amount of light incidentto an imaging plane 280.

The optical imaging system 200 includes a filter 270. For example, thefilter 270 is disposed between the sixth lens 260 and the imaging plane280. The filter 270 disposed as described above filters infrared raysincident to the imaging plane 280.

The optical imaging system 200 includes an image sensor. The imagesensor provides the imaging plane 280 on which light refracted throughthe lenses is imaged. In addition, the image sensor converts an opticalsignal imaged on the imaging plane 280 into an electrical signal.

The optical imaging system, configured as described above, representaberration characteristics as illustrated in FIG. 5. FIG. 6 is a tablerepresenting characteristics of lenses of the optical imaging system,according to an embodiment.

An optical imaging system, according to a third embodiment will bedescribed with reference to FIG. 7.

The optical imaging system 300, according to the third embodiment,includes a plurality of lenses having refractive power. For example, theoptical imaging system 300 includes a first lens 310, a second lens 320,a third lens 330, a fourth lens 340, a fifth lens 350, and a sixth lens360.

In accordance with an example, the object-side surfaces and theimage-side surfaces to be described below with respect to each of thefirst through sixth lenses 310 through 360 are described with respect tothe paraxial regions. For instance, for the first lens 310, anobject-side surface thereof is convex in the paraxial region and animage-side surface thereof is concave in the paraxial region. Surfaceregions, on the object-side surface and the image-side surface, whichneighbor or are in the vicinity of the paraxial regions may also havethe same curvature as the corresponding paraxial regions or may beconcave, convex, flat, or substantially flat. The configurationillustrated in FIG. 3 is one illustrative example of the surface regionsin the vicinity of the paraxial regions. However, a person skilled inthe art will appreciate that different curvatures or flatness may beimplemented in the surface regions in the vicinity of the paraxialregions than those illustrated in FIG. 3.

The first lens 310 has a positive refractive power, and an object-sidesurface thereof is convex and an image-side surface thereof is concave.The second lens 320 has a positive refractive power, and an object-sidesurface thereof is convex and an image-side surface thereof is convex.The third lens 330 has a negative refractive power, and an object-sidesurface thereof is convex and an image-side surface thereof is concave.The fourth lens 340 has a positive refractive power, and an object-sidesurface thereof is convex and an image-side surface thereof may beconcave. The fifth lens 350 does not have refractive power in a paraxialregion thereof. For example, the fifth lens 350 has a plane in theparaxial region thereof. In one embodiment, the fifth lens 350 is aplane in the paraxial region of the object-side surface thereof and theparaxial region of the image-side surface thereof. In anotherembodiment, the fifth lens 350 is a plane in the paraxial region only ofthe object-side surface thereof. In further another embodiment, thefifth lens 350 is a plane in the paraxial region only of the image-sidesurface thereof.

The sixth lens 360 has a negative refractive power, and an object-sidesurface thereof is convex and an image-side surface thereof is concave.In addition, inflection points are formed on both surfaces of the sixthlens 360. For example, the object-side surface of the sixth lens isconvex in a paraxial region thereof and concave in the vicinity of theparaxial region. Similarly, the image-side surface of the sixth lens isconcave in a paraxial region thereof and convex in the vicinity of theparaxial region.

The optical imaging system 300 includes a stop ST. For example, the stopST is disposed between the second lens 320 and the third lens 330. Thestop ST disposed as described above adjusts an amount of light incidentto an imaging plane 380.

The optical imaging system 300 includes a filter 370. For example, thefilter 370 is disposed between the sixth lens 360 and the imaging plane380. The filter 370 disposed as described above filters infrared raysincident to the imaging plane 380.

The optical imaging system 300 includes an image sensor. The imagesensor provides the imaging plane 380 on which light refracted throughthe lenses is imaged. In addition, the image sensor converts an opticalsignal imaged on the imaging plane 380 into an electrical signal.

The optical imaging system, configured as described above, representsaberration characteristics as illustrated in FIG. 8. FIG. 9 is a tablerepresenting characteristics of lenses of the optical imaging system,according to an embodiment.

Table 1 represents values of Conditional Expressions 1 through 7 of theoptical imaging systems according to the first to third embodiments. Asseen in Table 1, the optical imaging systems according to the first tothird embodiments may satisfy all of numerical according to ConditionalExpressions 1 through 7, as described above.

TABLE 1 Conditional First Second Third Expression Embodiment EmbodimentEmbodiment Th5/f 0.1550 0.1559 0.1926 V1 − V3 34.600 34.600 34.600|Sag51/Th5| 0.8862 0.8862 0.7093 f3/f2 −1.3290 −1.3311 −1.2995 OAL/f1.1888 1.1911 1.1797 n5 1.6500 1.6500 1.6500 F number 1.8000 1.80001.8000

As set forth above, according to various embodiments, a clear image isrealized.

While this disclosure includes specific examples, it will be apparent toone of ordinary skill in the art that various changes in form anddetails may be made in these examples without departing from the spiritand scope of the claims and their equivalents. The examples describedherein are to be considered in a descriptive sense only, and not forpurposes of limitation. Descriptions of features or aspects in eachexample are to be considered as being applicable to similar features oraspects in other examples. Suitable results may be achieved if thedescribed techniques are performed in a different order, and/or ifcomponents in a described system, architecture, device, or circuit arecombined in a different manner and/or replaced or supplemented by othercomponents or their equivalents. Therefore, the scope of the disclosureis defined not by the detailed description, but by the claims and theirequivalents, and all variations within the scope of the claims and theirequivalents are to be construed as being included in the disclosure.

What is claimed is:
 1. An optical imaging system, comprising: a firstlens comprising positive refractive power and a concave image-sidesurface; a second lens comprising positive refractive power; a thirdlens comprising negative refractive power and a convex object-sidesurface; a fourth lens comprising a refractive power; a fifth lenscomprising a refractive power; a sixth lens comprising negativerefractive power, a convex object-side surface, and an inflection pointformed on an image-side surface of the sixth lens, wherein the first tosixth lenses are sequentially disposed from an object side toward animaging plane, wherein the fourth lens has a concave object-side surfaceor the fifth lens has a concave image-side surface, wherein a thicknessof the first lens is greater than a thickness of the second lens,wherein a distance from the image-side surface of the first lens to anobject-side surface of the second lens is greater than a distance fromthe image-side surface of the fifth lens to the object-side surface ofthe sixth lens, and wherein a radius of curvature of an object-side ofthe third lens is greater than a radius of curvature of an object-sideof the second lens.
 2. The optical imaging system of claim 1, whereinthe first lens has a convex object-side surface.
 3. The optical imagingsystem of claim 1, wherein the second lens has a convex object-sidesurface.
 4. The optical imaging system of claim 1, wherein the fourthlens comprises positive refractive power.
 5. The optical imaging systemof claim 1, wherein 0.05<Th5/f<0.25 is satisfied, in which Th5 is athickness of an optical axis center of the fifth lens, and f is anoverall focal length of the optical imaging system.
 6. The opticalimaging system of claim 1, wherein 20<V1−V3<70 is satisfied, in which V1is an Abbe number of the first lens, and V3 is an Abbe number of thethird lens.
 7. The optical imaging system of claim 1, wherein −1.5<f3/f2is satisfied, in which f2 is a focal length of the second lens, and f3is a focal length of the third lens.
 8. The optical imaging system ofclaim 1, wherein 0.5<OAL/f<2.0 is satisfied, in which OAL is a distancefrom an object-side surface of the first lens toward the imaging plane,and f is an overall focal length of the optical imaging system.
 9. Theoptical imaging system of claim 1, wherein a radius of curvature of theobject-side surface of the third lens is greater than a radius ofcurvature of the image-side surface of the first lens.
 10. The opticalimaging system of claim 1, wherein a radius of curvature of animage-side surface of the third lens is greater than a radius ofcurvature of the object-side surface of the sixth lens.